Organic Dye-Doped PMMA Lasing

Organic thin-film lasers gain interest as potential light sources for application in diverse fields. With the current development, they hold variety of benefits such as: low-cost, high-performance, and color-tunability. Meanwhile, the production is not complicated because both the resonator and the gain medium can be assembled by solution-processable organic materials. To our knowledge, information about using poly(methyl methacrylate) (PMMA) as a matrix for organic dye lasers was insubstantial. Herein, the feasibility of using organic dye-doped PMMA as an organic dye laser was tested. Six different sample designs were introduced to find out the best sample model. The most optimum result was displayed by the sample design, in which the gain medium was sandwiched between the substrate and the photoresist layer with grating structure. The impact of dye concentration and grating period on peak wavelength was also investigated, which resulted in a shift of 6 nm and 25 nm, respectively. Moreover, there were in total six various organic dyes that could function well with PMMA to collectively perform as ’organic dye lasers’, and they emitted in the range of 572 nm to 609 nm. Besides, one of the samples was used as a sensor platform. For instance, it was used to detect the concentration of sugar solutions.

INVESTIGATION OF THE SPECTRUM OF ZN I ATOMS IN THE TRIPLET RYDBERG STATES

Purpose: This work aims at investigating the zinc atoms in the triplet preionization – Rydberg states. The energy levels of atoms having two electrons outside the closed shell were studied mainly by the optical spectroscopy methods. However, just using the microwave spectroscopy to measure the frequency of transitions between the two Rydberg states allows to increase the accuracy of measurements in two or more orders of magnitude. Disign/methodology/approach:A line of three dye lasers is used to excite the zinc atoms into the triplet Rydberg states with a predetermined set of quantum numbers. The radiation of the first two of them is transformed into the second harmonic in nonlinear crystals. Dye lasers are excited by the radiation of the second harmonic of one YAG: ND3+ laser. All three radiations are reduced to the zone of interaction with the laser and the microwave radiation, which is located between the plates of the ionization cell, where the pulsed electric field is created. The excited Rydberg atoms are recorded with the field ionization procedure. The beam of neutral atoms is created by an effusion cell under the vacuum conditions, the residual pressure does not exceed 10-5 mm Hg. A pulsed electric field of some certain intensity results inionization of atoms excited by microwave radiation and in acceleration of electrons, which have appeared in the direction of the secondary electron multiplier, though being insufficient for ionization of atoms excited only by the laser radiation and which are initial for interaction with microwaves. By scanning the microwave radiation frequency with the given step and measuring the signal intensity of the secondary electron multiplier, the excitation spectrum of the atoms under study can be obtained. Findings: Using the created laser-microwave spectrometer, the frequencies of the F→D, F→F and F→G transitions between the triplet Rydberg states of zinc atoms were measured. From the analysis made of the transition frequencies, the quantum defect decomposition constants were obtained by the Ritz formula for the D, F, and G states of zinc atoms. Conclusions: The frequencies of the F→D, F→F and F→G transitions between the triplet Rydberg states of zinc atoms were measured that allowed obtaining the quantum defect decomposition constants according to the Ritz formula for the D, F and G states of zinc atoms, that in turn had allowed to calculate the energy of these terms and the transition frequencies at least in two orders of magnitude more accurately as against the similar measurements made by the optical spectroscopy. Key words: zinc atom, triplet states of atoms, Rydberg states, laser excitation, microwave radiation

Photonic Crystal Polymeric Thin-Film Dye-Lasers for Attachable Strain Sensors

In this report, using two-dimensional photonic crystals (PhC) and a one-dimensional PhC nano-beam cavity, we realized the development of all-polymeric dye-lasers on a dye-doped, suspended poly-methylmethacrylate film with a wavelength-scale thickness. In addition to the characterization of basic lasing properties, we also evaluated its capacity to serve as an attachable strain sensor. Through experimentation, we confirmed the stable lasing performances of the dye-laser attaching on a rough surface. Moreover, we also theoretically studied the wavelength responses of the utilized PhC resonators to stretching strain and further improved them via the concept of strain shaping. The attachability and high strain sensing response of the presented thin film PhC dye-lasers demonstrate their potential as attachable strain sensors.

37 Analysis of the Utility of CO2 and Pulse-Dye Lasers in the Treatment of Hypertrophic Burn Scars

Introduction Despite advances in burn care, hypertrophic burn scars (HTBS) remain a significant source of morbidity. Treatment often involves use of CO2 lasers to reduce thickness and pulse-dye lasers (PDL) to reduce erythema. Despite frequent utilization, little quantitative data exists. This study seeks to objectively determine the effects of these laser treatments on burn scars. Methods Patients found to have HTBS undergoing laser treatments were approached for enrollment. Following enrollment, an area of HTBS outside of the treatment area was divided into 4 equal 3x3cm squares which were randomized to receive either CO2, PDL, CO2+PDL, or no treatment. Patients underwent a total of 3 treatments, 4–6 weeks apart, and were seen for follow-up over 3–6 months. Scar assessments occurred at each visit prior to treatment and consisted of digital photographs, ultrasound assessment for scar thickness, colorimetry, and the Patient and Observer Scar Assessment Score (POSAS). Results Twenty-five patients were enrolled at our institution. To date, 12 (48%) have completed all 3 treatments and the remainder are still in their follow-up period. Median initial scar thickness (ST) was 0.3cm. Mean time since injury was 9 months. Overall, there was a significant decrease in ST over time (p=0.0246) but not between treatment groups. There were no significant changes seen in melanin, erythema, or POSAS scores (p=0.9030, 0.6470, and 0.1495, respectively). When separated by ST before initiation of treatment, thin scars (< 3cm) appeared to be overall less erythematous in groups treated with PDL and CO2+PDL and untreated groups (p=0.0358, 0.0027. 0.0118, respectively) as compared to thick scars (≥3cm). Thin scars treated with PDL and CO2+PDL were also less pigmented than thick scars (p=0.0127, 0.0213, respectively). Erythema significantly decreased between the last treatment and the final visit for PDL and CO2+PDL groups (p< 0.0001). Older scars (≥9 months prior to treatment) tended to have a greater reduction in thickness as compared to newer scars but the difference was not significant to date. Conclusions Laser therapy is often employed in the treatment of HTBS. However, few studies have determined their objective benefits. Based on a preliminary analysis of our data, we have shown an overall decrease in scar thickness, less pigmentation, and less erythema in thin scars treated with PDL or CO2+PDL. Further analysis will be performed after additional follow-up information is collected.

Active media based on polyurethane doped with a binary dye mixture

Subject and Purpose. The article is concerned with the spectral-luminescent and lasing characteristics of the radiation from solid-state active media based on polyurethane activated by a binary mixture of dyes. The purpose of these studies is to demonstrate a possibility of the spectral range expansion of the emission from solid-state dye lasers with polyurethane active elements. Methods and Methodology. Specially prepared samples of polyurethane active media having the same donor (Rhodamine 6G) concentration but various acceptor (Sulforhodamine 101) concentrations are experimentally studied for their spectral-luminescent and lasing characteristics. Results. The main spectroscopic characteristics of Rhodamine 6G and Sulforhodamine 101 in polyurethane have been measured, the nonradiative energy transfer parameters in this molecular pair estimated. It has been demonstrated that the matrix emission spectrum can be purposefully transformed by selection of relative concentrations of dyes in the mixture. In a broadband resonator, either a single- or two-band emission with different positions and various intensities of spectral bands is observed depending on the acceptor concentration. In a dispersive resonator under the same conditions, the tuning range of the lasing spectrum expands and extends to the longer wavelengths. Conclusion. The prospects of using donor-acceptor dye mixtures for improving spectral characteristics of polyurethane active elements in solid-state dye lasers have been confirmed. It has been shown that signatures of the emission characteristics of these media are governed by the mechanism of the excitation energy transfer between dye molecules. Lasing has been obtained on polyurethane matrices with the emission wavelength tuning throughout the “green-red” region of the spectrum.

Isotope separation of 176Lu a precursor to 177Lu medical isotope using broadband lasers

A new photoionization scheme accessible by Rhodamine dye lasers is proposed for the isotopeseparation of 176Lu. 5d6s2 2D3/2 (0.0 cm-1) - 573.8130 nm -> 5d6s6p 4Fo3/2 (17427.28 cm-1) - 609.6007 nm -> 6s6p2 4P3/2 (33831.46 cm-1) ---> Autoionization State---> Lu+ Optimum conditions for the isotope separation have been derived and compared with thepreviously reported work. The enrichment of ~ 49% can be obtained with > 12 mg / hourproduction rates even when broadband lasers with bandwidth of 500 MHz employed for the twostep excitation. The simplified system requirements for the photoionization scheme with a highproduction rate is expected reduce the global shortage of 176Lu for medical applications.

A Palette of Efficient and Stable Far-Red and NIR Dye Lasers

The disposal of long-wavelength-emitting sources is of paramount relevance in technology and biophotonics due to the low interference with the surroundings that these kinds of far-red and near-infrared radiations hold. As a result of the continued efforts carried out during the last few years by our research group to design new boron-dipyrromethene (BODIPY) dyes with improved photonic performance, two approaches were tested to develop a new generation of organic dyes able to display efficient and long-lasting laser emission in both target spectral regions. On the one hand, the annulation of aromatic benzofuran at the dipyrrin backbone leads to conformationally restricted dyes yielding photostable and bright laser emission beyond 600 nm at the far-red spectral region. On the other hand, a more pronounced shift to longer wavelengths reaching 725 nm at the near-infrared region is feasible, while keeping a reasonably high laser efficiency and tolerance to prolonged and intense pumping, based on aza-BODIPYs bearing peripheral aryl rings. These two complementary strategies yield a library of laser-emitting compounds comprising the 600–725 nm spectral region. Moreover, their laser performance is better than the commercially available dye lasers active in this spectral window.